11/21/2000Information Organization and Retrieval Thesaurus Design and Development University of California, Berkeley School of Information Management and Systems SIMS 202: Information Organization and Retrieval

11/21/2000Information Organization and Retrieval Review Name Authority Control Types of Controlled Vocabularies Categories and Categorization Interface Design

11/21/2000Information Organization and Retrieval Types of Indexing Languages Uncontrolled Keyword Indexing Indexing Languages –Controlled, but not structured Thesauri –Controlled and Structured Classification Systems –Controlled, Structured, and Coded Faceted Classification Systems

11/21/2000Information Organization and Retrieval Uses of Controlled Vocabularies Library Subject Headings, Classification and Authority Files. Commercial Journal Indexing Services and databases Yahoo, and other Web classification schemes Online and Manual Systems within organizations –SunSolve –MacArthur

11/21/2000Information Organization and Retrieval Indexing Languages An index is a systematic guide designed to indicate topics or features of documents in order to facilitate retrieval of documents or parts of documents. An Indexing language is the set of terms used in an index to represent topics or features of documents, and the rules for combining or using those terms.

11/21/2000Information Organization and Retrieval Classification Systems A classification system is an indexing language often based on a broad ordering of topical areas. Thesauri and classification systems both use this broad ordering and maintain a structure of broader, narrower, and related topics. Classification schemes commonly use a coded notation for representing a topic and it’s place in relation to other terms.

11/21/2000Information Organization and Retrieval Automatic Indexing and Classification Automatic indexing is typically the simple deriving of keywords from a document and providing access to all of those words. More complex Automatic Indexing Systems attempt to select controlled vocabulary terms based on terms in the document. Automatic classification attempts to automatically group similar documents using either: –A fully automatic clustering method. –An established classification scheme and set of documents already indexed by that scheme.

11/21/2000Information Organization and Retrieval Clustering Agglomerative methods: Polythetic, Exclusive or Overlapping, Unordered clusters are order-dependent. Doc 1. Select initial centers (I.e. seed the space) 2. Assign docs to highest matching centers and compute centroids 3. Reassign all documents to centroid(s) Rocchio’s method – (Yes the same Rocchio as Relevance Feedback)

11/21/2000Information Organization and Retrieval Automatic Class Assignment Doc Search Engine 1. Create pseudo-documents representing intellectually derived classes. 2. Search using document contents 3. Obtain ranked list 4. Assign document to N categories ranked over threshold. OR assign to top-ranked category Automatic Class Assignment: Polythetic, Exclusive or Overlapping, usually ordered clusters are order-independent, usually based on an intellectually derived scheme

11/21/2000Information Organization and Retrieval Today Developing Controlled Vocabularies Thesaurus design Steps in Thesaurus development Indexing

11/21/2000Information Organization and Retrieval Developing Controlled Vocabularies Origins and Uses of Controlled Vocabularies for Information Retrieval Types of Indexing Languages, Thesauri and Classification Systems Process of Design and Development of Thesauri

11/21/2000Information Organization and Retrieval Origins Very early history of content representation –Sumerian tokens and “envelopes” –Alexandria - pinakes –Indices

11/21/2000Information Organization and Retrieval Origins Biblical Indexes and Concordances –Hugo de St. Caro – 1247 A.D. : 500 Monks -- KWOC –Book indexes (Nuremburg Chronicle) Library Catalogs Journal Indexes “Information Explosion” following WWII –Cranfield Studies of indexing languages and information retrieval –Development of bibliographic databases Index Medicus -- production and Medlars searching

11/21/2000Information Organization and Retrieval Origins Communication theory revisited Problems with transmission of meaning Noise SourceDecodingEncodingDestination Message Channel StorageSource Decoding (Retrieval/Reading) Encoding (writing/indexing) Destination Message

11/21/2000Information Organization and Retrieval Structure of an IR System Search Line Interest profiles & Queries Documents & data Rules of the game = Rules for subject indexing + Thesaurus (which consists of Lead-In Vocabulary and Indexing Language Storage Line Potentially Relevant Documents Comparison/ Matching Store1: Profiles/ Search requests Store2: Document representations Indexing (Descriptive and Subject) Formulating query in terms of descriptors Storage of profiles Storage of Documents Information Storage and Retrieval System Adapted from Soergel, p. 19

11/21/2000Information Organization and Retrieval What is a “Controlled Vocabulary” “The greatest problem of today is how to teach people to ignore the irrelevant, how to refuse to know things, before they are suffocated. For too many facts are as bad as none at all.” (W.H. Auden) Similarly, there are too many ways of expressing or explaining the topic of a document. Controlled vocabularies are sets of Rules for topic identification and indexing, and a THESAURUS, which consists of “lead-in vocabulary” and an limited and selective “Indexing Language” sometimes with special coding or structures.

11/21/2000Information Organization and Retrieval Thesauri A Thesaurus is a collection of selected vocabulary (preferred terms or descriptors) with links among Synonymous, Equivalent, Broader, Narrower and other Related Terms

11/21/2000Information Organization and Retrieval Thesauri (cont.) National and International Standards for Thesauri –ANSI/NISO z American National Standard Guidelines for the Construction, Format and Management of Monolingual Thesauri –ANSI/NISO Draft Standard Z x -- American National Standard Guidelines for Indexes in Information Retrieval –ISO Documentation -- Guidelines for the establishment and development of monolingual thesauri –ISO Documentation -- Guidelines for the establishment and development of multilingual thesauri

11/21/2000Information Organization and Retrieval Thesauri (cont.) Examples: –The ERIC Thesaurus of Descriptors –The Art and Architecture Thesaurus –The Medical Subject Headings (MESH) of the National Library of Medicine

11/21/2000Information Organization and Retrieval Why develop a thesaurus? To provide a conceptual structure or “space” for a body of information –To make it possible to adequately describe the topical contents of informational objects at an appropriate level of generality or specificity –To provide enhanced search capabilities and to improve the effectiveness of searching (I.e., to retrieve most of the relevant material without too much irrelevant material).

11/21/2000Information Organization and Retrieval Why develop a thesaurus? To provide vocabulary (or terminological) control. –When there are several possible terms designating a single concept, the thesaurus should lead the indexer or searcher to the appropriate concept, regardless of the terms they start with.

11/21/2000Information Organization and Retrieval Preliminary considerations What is used now? –Continue using an existing thesaurus? –Ad hoc modification of existing thesaurus? –Develop a new well-structured thesaurus? What is the scope and complexity of the subject field? What kind of retrieval objects or data will be dealt with? How exhaustive and specific is the desired description of objects?

11/21/2000Information Organization and Retrieval Preliminary Considerations The scope and complexity of the field will provide some indication of the scope and complexity of the thesaurus. –It is better to plan for a larger and more comprehensive system than a smaller system that rapidly will become inadequate as the database grows. Development of a good thesaurus requires a major intellectual effort as well as clerical operations like data entry and production of sorted lists.

11/21/2000Information Organization and Retrieval Development of a Thesaurus Term Selection. Merging and Development of Concept Classes. Definition of Broad Subject Fields and Subfields. Development of Classificatory structure Review, Testing, Application, Revision.

11/21/2000Information Organization and Retrieval Flow of Work in Thesaurus Construction Select Sources Assign codes Select Terms Record Selected Terms Sort Terms Merge identical Terms Define Broad Subject Fields Merge Terms in Same Concept class Sort Terms into Broad Subject Fields Define Subfields within one Subject Field Work out detailed structure of the Subject Field Select Preferred Terms All Subfields of Broad Subject finished? All Broad Subjects finished? Improve Class Structure Yes No Print Classified Index and review Discuss with Experts and Users Select descriptors and checklist items Produce Full Thesaurus and Check references Assign Notation Review and Test Many Modifications? Based on Soergel, pp Yes No Revise as needed

11/21/2000Information Organization and Retrieval 1. Term Selection Select sources for the collection of terms. –Prearranged Sources –Open-ended Sources Assign codes to each source. Selection of terms –For part of pre- arranged and for all open-ended sources Enter terms into database with all information.

11/21/2000Information Organization and Retrieval 1.1 Kinds of Sources Prearranged Sources –Existing descriptor lists, classification schemes thesauri. This includes universal schemes like DDC or LCSH. –Nomenclatures of single disciplines –Treatises on the terminology of a field –Encyclopedias, lexica, dictionaries and glossaries. –Tables of contents of textbooks and handbooks –Indexes of journals or abstracting journals –Indexes of other publications in the field

11/21/2000Information Organization and Retrieval 1.1 Kinds of Sources Open-ended sources –Lists of search requests or interest profiles –Description of projects/activities to be served by the information retrieval system. –Discussion with specialists in the field –Sample of documents in the field Ask users why and how these documents relate to the field. Have documents indexed by experts in the field –Lists of titles of documents in the field –Abstracts and reviews of documents –Your own knowledge

11/21/2000Information Organization and Retrieval Selection of sources Prearranged sources require less effort in gathering the material, and may already indicate some relationships between terms and concepts and relationships among terms. Open-ended sources can reflect current terminology and may provide more complete coverage. Choose a set of sources that are current, as complete as possible, and considered authoratative.

11/21/2000Information Organization and Retrieval Selection of Sources Each selected source is assigned an ID for tracking its use in the development of the thesaurus. –Useful when making decisions about which terms to prefer –Useful for backtracking when questions arise (where did this come from?)

11/21/2000Information Organization and Retrieval Selection of Terms Terms can be transferred directly from prearranged sources to the recording medium (cards or database) –Have to decide which terms and references to include, or to take the whole source

11/21/2000Information Organization and Retrieval Selection of Terms In open-ended sources you read through the source and pick out terms (I.e. words and phrases) that might be useful in retrieval or as references to other terms. Alternatively, use keyword and phrase extraction software to create lists of terms and select from those. Transfer selected terms to the recording medium (cards or database).

11/21/2000Information Organization and Retrieval 2. Merging and Development of Concept Classes Sort Term DB into alphabetical order. First Round: Merge information for Identical terms -- possibly pulling info from additional sources. Second Round: Merge synonyms or terms in the same concept class.

11/21/2000Information Organization and Retrieval 3. Definition of Broad Subject Fields and Subfields Define Broad Subject fields and sort terms into these broad fields Define subfields within each broad field and sort terms into these subfields. Work out the detailed structure –Select Preferred Terms –Merge information for terms in the same concept class Repeat these steps –for each subfield within a broad field –and for each broad field –Until all terms have been consolidated and preferred terms selected

11/21/2000Information Organization and Retrieval 4. Development of Classificatory Structure Produce preliminary version of classified index and update the working database. Improve classificatory structure Reality check: produce and distribute a version of the classified index. Distribute to users/experts.

11/21/2000Information Organization and Retrieval 5. Final Stages Review Testing Application Revision

11/21/2000Information Organization and Retrieval Review Discuss classified index with users/experts. –Select descriptors and checklist descriptors. Assign Notational Symbols Produce Main Thesaurus & Indexes

11/21/2000Information Organization and Retrieval Review (cont.) Check cross references and insert where needed Produce Test Version Test by Indexing Modify as needed Produce Production Version.

11/21/2000Information Organization and Retrieval Testing a Thesaurus Assign descriptors to a sample set of NEW documents (use enough to get an idea of any gaps in the thesaurus. Test retrieval using sample questions and seeing how effectively the thesaurus maps to the appropriate descriptor

11/21/2000Information Organization and Retrieval The Indexing Process Concept identification term selection (via thesaurus) term assignment

11/21/2000Information Organization and Retrieval Application: The Indexing Process (Manual) Is Term suitable NO Select Alternative term to represent Concept Would Concept be better represented by one of these terms Is There Another Concept Consider Preferred Term Select Preferred Term Establish Term Denoting Concept Examine Document and Identify Significant Concepts Consider First Concept Preferred Term? Start NO YES Does Thesaurus contain term for Concept Consider any associated terms in Thesaurus (NT,BT) Admit New Term Into Thesaurus Can Concept be expressed combining terms? Consider Each of These Terms Assign Terms to Document Prefer Alternative Term(s) End Adapted from ISO 5963, p.5

11/21/2000Information Organization and Retrieval Thesaurus Revision and Updates There will always be new concepts, products, or expressions that need to be added to the thesaurus. –Set a regular schedule of reviews and revisions. –Collect complaints, problems, etc. and fold into revision of the thesaurus

11/21/2000Information Organization and Retrieval References Soegel, D. Indexing Languages and Thesauri: Construction and Maintenance. Los Angeles : Melville Publishing Co., 1974 Foskett, A.C. The Subject Approach to Information. London: Clive Bingley, Standards: –ANSI/NISO z American National Standard Guidelines for the Construction, Format and Management of Monolingual Thesauri –ANSI/NISO Draft Standard Z x -- American National Standard Guidelines for Indexes in Information Retrieval –ISO Documentation -- Guidelines for the establishment and development of monolingual thesauri –ISO Documentation -- Guidelines for the establishment and development of multilingual thesauri